The increased number of light emitting devices including LEDs (light emitting diodes) or other types of semiconductor components as light emitting components is used in recent years. Researches have been conducted on such light emitting devices for application thereof to light sources of backlight for liquid crystal displays because of high initial-driving performances and tolerances to vibration and repeated switching between on and off.
An example of light emitting device circuit configuration is disclosed in Patent Document 1. In light emitting devices having similar configurations as the one in Patent Document 1, power losses may increase depending on circuit configurations of the light emitting devices. This is because different control is required for those devices from devices including CCFLs (cold cathode fluorescent lamp) as light sources, which are conventional light sources of backlights. When the power losses increase, the amounts of heat generated during power consumption increase resulting in temperatures increases in the light emitting device. Therefore, some kind of measures to reduce the temperatures of the light emitting device, such as a heatsink, is required.
A technology for reducing a power loss in the light emitting device is disclosed in Patent Document 1. According to the technology, the power loss is reduced by the following method. In a circuit for driving sets of light emitting components in which light emitting components are connected in series, forward voltages in the sets are measured and a common voltage applied to the sets is properly adjusted.